1. Field of the Invention
The present invention relates to an internal combustion engine of the type in which fuel is directly injected into a combustion chamber and both a phase of the center (it will be hereinafter referred to as “center phase” for the simplicity sake) of an operating angle of an intake valve and an effective opening area (i.e., a lift amount) of the intake valve are variably controlled. More particularly, the present invention relates to an apparatus for and a method of controlling an intake operation of an internal combustion engine of the described type.
2. Description of the Related Art
Japanese Laid-open (Kokai) Patent Application Publication No. 2005-140007 discloses such a technical idea that, in a direct-injection type internal combustion engine, the lift amount of an intake valve is controlled to become lower during a period of time from the starting of an engine operation to a time before completion of the engine warming-up, in order to reduce engine friction and to accelerate vaporization of injected fuel by increasing a flow velocity of intake air.
Further, similarly to the above-mentioned technical idea, WO97/13063 discloses an art in which the fuel injection is performed in an intake stroke while controlling a lift amount of an intake valve to become lower, in order to accelerate vaporization of injected fuel by increasing the flow velocity of intake air at the time of starting of the engine.
However, according to Japanese Laid-open (Kokai) Patent Application Publication No. 2005-140007, when characteristics of the direct-injection type internal combustion engine are utilized to perform the warming-up accelerating combustion by which ignition timing and injection timing are retarded until an expansion stroke so that the exhaust gas temperature is increased, since a required air amount is large, the lift amount of the intake valve cannot be controlled to become low, and consequently, an increase in the flow velocity of the intake air cannot be achieved.
Further, as described in WO97/13063, even if the lift amount of the intake valve can be controlled to become low, the intake stroke is completed before a negative pressure fully prevails in a combustion chamber. Therefore, a period of time in which the flow velocity of intake air is high is too short to complete the fuel injection during this short period of time.